"C-6. Rhodochrosite. Catamarca Provenee, Argentina (67, hand-ground).
Rhodochrosite, MnCO3, is a comparatively rare carbonate mineral,
usually occurring in hydrothermal veins with ores of silver, lead and
copper, and with other manganese minerals. Divalent iron and calcium
substitute for manganese, and a complete solid solution series appears
to extend to siderite and calcite. This particular sample displays the
rich pink color in hand specimen that is typical of pure rhodochrosite.
It is, however, very rare to find rhodochrosite free of iron, and this
sample is no exception. It does, in fact, contain 1% iron, and displays
a fairly strong ferrous ion band near 1.1µ, in addition to the
typical near-infrared carbonate bands. The bands in the visible, on the
other hand, are due to the manganese ion, and are unusually sharp
electronic transition bands, as discussed and assigned in the previous
section, entitled "Spectral Features of Carbonates"."